The present invention relates to a device for moving members into engagement with a workpiece to engage the workpiece. In particular, the present invention relates to a device for moving workpiece gripping jaws toward and away from each other.
Devices for moving members into engagement with a workpiece are used in many types of material handling equipment and are used in robotics. It is important in operation of such devices that the jaws or other workpiece engaging elements move synchronously. It is also important that the devices be light in weight and efficient in operation.
Devices which provide synchronized movement of jaw members are known. In many of the known devices, each jaw member is associated with a rack, and the two racks engage a common pinion so that the two jaws must move in unison. Such a device is shown, for example, in U.S. Pat. No. 2,679,177. Such devices are relatively heavy and cumbersome.
Another type of device for moving jaws in a synchronized manner is shown in U.S. Pat. No. 3,899,162. This patent discloses jaw moving members which have faces which engage a synchronization member. The synchronization member is movable in a direction at a right angle to the direction of movement of the jaws. When the jaws move toward each other, the jaws contact the synchronization member and move the member against the resistance of a spring. The synchronization member insures that the jaws move toward each other in a synchronous manner. In such a device, friction forces are created acting transverse to the direction of jaw movement. These friction forces must be overcome by the fluid cylinders which move the jaws. This device, also, requires a number of elements (synchronization member, two cylinders, a spring). Thus, such a device is also relatively heavy.
Another means for effecting synchronization of jaw movement is shown in U.S. Pat. No. 3,727,772. In this patent, two double-acting cylinders move jaw members. In this structure the pistons are stationary and the cylinders move. The cylinders move along two parallel feed screws arranged symmetrically with respect to an axis common to both cylinders. The screws have oppositely inclined mirror symmetrical threads meshing with internal threads provided on nuts located in each cylinder body. Upon axial movement of the cylinders, the screws rotate. This insures synchronized movement of the jaws. The structure of U.S. Pat. No. 3,727,772 is rather complicated and because of the number of parts is cumbersome to manufacture and is not light in weight.